@Marvin Is it possible to define the task runner for a given flow from the flow parameters?

Yes, it is possible to define the task runner for a given flow in Prefect. You can specify a task runner when defining a flow to control how tasks are executed. Prefect provides several task runners, such as

ThreadPoolTaskRunner

,

DaskTaskRunner

, and

RayTaskRunner

, which can be used for concurrent, parallel, or distributed task execution. Here's a simple example of how you might define a task runner for a flow:

python
from prefect import flow
from prefect.task_runners import ThreadPoolTaskRunner

@flow(task_runner=ThreadPoolTaskRunner())
def my_flow():
    # Define your tasks here
    pass

In this example,

ThreadPoolTaskRunner

is used to run tasks concurrently within a thread pool. You can replace it with other task runners like

DaskTaskRunner

or

RayTaskRunner

based on your requirements. For more information, you can refer to the Prefect Task Runners documentation. If you have any specific requirements or need further assistance, feel free to ask!

Sure @Marvin but can I replace the task_runner at run time?

In Prefect 3.x, you cannot directly change the task runner for a flow at runtime. However, you can achieve similar functionality by using nested flows with different task runners. This allows you to configure specific tasks or groups of tasks to run with different task runners based on your requirements. Here's an example of how you might use nested flows to achieve this:

python
from prefect import flow
from prefect.task_runners import ThreadPoolTaskRunner, DaskTaskRunner

@flow(task_runner=ThreadPoolTaskRunner())
def main_flow():
    # This flow uses ThreadPoolTaskRunner by default
    # Call a nested flow with a different task runner
    nested_dask_flow()

@flow(task_runner=DaskTaskRunner())
def nested_dask_flow():
    # This flow uses DaskTaskRunner
    # Define tasks that benefit from parallel execution
    pass

if __name__ == "__main__":
    main_flow()

In this setup,

main_flow

uses

ThreadPoolTaskRunner

, while

nested_dask_flow

uses

DaskTaskRunner

. This allows you to execute different parts of your workflow with different task runners, effectively adapting to runtime needs. For more details, you can refer to the Prefect Task Runners documentation.

Thanks @Marvin

You're welcome. If you have any more questions or need further assistance, feel free to ask. Though it's a bit of a drag, I'm here to help.